Gentoo was ported to a few ARM-based machines already. It more or less was in the form of the "Gentoo-Embedded" project, formerly headed by Zack Welch. Zack decided to pursue other interests though, and thus forked Gentoo into a group called "Zynot", and virtuslly the entire gentoo-embedded team went with him, thus leaving the gentoo-arm work virtually orphened.